Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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        Alkaptonuria
      

Ochronosis is the deposition of pigmented product in tissues and can be of genetic type (endogenous) or acquired (exogenous) in skin via bleaching agents.

While we don't know whether there are degrees of penetrance in expression of this rare genetic disease, one must presume the possibility of such. From a surgical pathology standpoint, the most likely encounter of this problem is in skin biopsies for documentation of the homogentisic acid deposits on collagen as a complication of skin bleaching treatments (exogenous ochronosis). The most important detection is in joint or vertebral specimens from surgical intervention in younger-than-usual DJD surgery (dark color likely to be noted by surgeon...see vertebral specimens HERE). [CP11-31] At autopsy, we might see bone & cartilage changes & even dark sclerae. Skin biopsy might show brown-grey bodies.

In alkaptonuria cases, there is a 3q21 gene defect leading to systemic lack of homogentisic oxidase so that homogentisic acid accumulates and is increased in urinary excretion. When the urine hits air, the homogentisic acid is oxidized and turns dark...even black. This may lead to a black-stained baby diaper or adult urine that darkens on standing. If ochronosis is suspected, check lab for a urine sample to see if it has oxidized to a dark color; add a little 10% ferric chloride1 from histology special stain area &, if has alkaptonuria & positive for homogentisic acid spilling in urine, the urine will/should turn black. Otherwise, urine is forwarded to such as Mayo Clinic reference lab for metabolic screening.

References:

  1. Sister Laurine Graff, A Handbook of Routine Urinalysis, 1983, 284 pages.
  2. Robins and Cotran, Pathologic Basis of Disease 7th Edition, 2005, 1525 pages.

(posted 31 August 2011; update 5 September 2011)

 
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